This invention relates to the art of fabricating thermal heads for thermal recording which are used in various types of printers, plotters, facsimile, recorders and the like as a recording device. More specifically, the invention relates to a thermal head lapping apparatus that is used to lap (polish) protective layers or layers to be coated therewith on a thermal head in the process of fabricating the thermal head.
Thermal materials comprising a thermal recording layer on a substrate of a film or the like are used to record images produced in diagnosis by ultrasonic scanning (sonography).
This recording method, also referred to as thermal recording, eliminates the need for wet processing and offers several advantages including convenience in handling. Hence in recent years, the use of the thermal recording system is not limited to small-scale applications such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnoses such as CT, MRI and X-ray photography where large and high-quality images are required is under review.
As is well known, thermal recording involves the use of a thermal head having a glaze, in which heating elements comprising a heat-generating resistor and electrodes are arranged in one direction (main scanning direction) and, with the glaze urged at small pressure against a thermal material, the two members are moved relative to each other in an auxiliary scanning direction perpendicular to the main scanning direction, and energy is applied to the respective heating elements of the glaze in accordance with image data to be recorded which were supplied from an image data supply source such as MRI or CT in order to heat the thermal recording layer of the thermal material, thereby performing image recording through color formation.
A protective coating is formed on the surface of the glaze of the thermal head in order to protect the heat-generating resistor for heating the thermal material, the associated electrodes and the like. Therefore, it is this protective coating that contacts the thermal material during thermal recording and the heat-generating resistor heats the thermal material through this protective coating so as to perform thermal recording.
The protective coating is usually made of wear-resistant ceramics such as silicon nitride; however, during thermal recording, the surface of the protective coating is heated and kept in sliding contact with the thermal material, so it will gradually wear and deteriorate upon repeated recording.
If the wear of the protective coating progresses, density unevenness will occur on the thermal image or a desired protective strength can not be maintained and, hence, the ability of the protective coating to protect the heat-generating resistor is impaired to such an extent that the intended image recording is no longer possible (the head has lost its function).
Particularly in the applications such as the aforementioned medical use which require multiple gradation images of high quality, the trend is toward ensuring the desired high image quality by adopting thermal films with highly rigid substrates such as polyester films and also increasing the setting values of recording temperature (energy applied) and of the pressure at which the thermal head is urged against the thermal material. Under these circumstances, as compared with the conventional thermal recording, a greater force and more heat are exerted on the protective coating of the thermal head, making wear and corrosion (or wear due to corrosion) more likely to progress.
With a view to preventing the wear of the protective coating on the thermal head and improving its durability, a number of techniques have been considered. In an example, it is considered to use the ceramic protective layer described above in combination with a carbon-based protective layer (hereinafter referred to as a xe2x80x9ccarbon protective layerxe2x80x9d). The carbon protective layer has properties quite similar to those of diamond including a very high hardness and chemical stability, hence the carbon protective layer presents sufficiently excellent properties to prevent wear and corrosion which may be caused by sliding contact with thermal materials.
Unexamined Published Japanese Patent Application (KOKAI) No. 7-132628 discloses a thermal head which has a dual protective coating comprising a lower silicon-based compound layer and an overlying diamond-like carbon layer, said protective coating having wear and breakage significantly reduced, thereby ensuring that high-quality images can be recorded over an extended period of time.
In the process of fabricating the thermal head, the protective layers are very often subjected to lapping treatment (polishing treatment) for the purpose of improving the surface properties and the adhesion of the protective layers and preventing the image deterioration and the damage of the thermal material.
The irregularities on the surface to be coated with the carbon protective layer described above are easily reflected thereon. Then, if the surface to be coated has irregularities, they are formed on the surface of the carbon protective layer, which would be a cause of image deterioration. The carbon protective layer is also brittle because of its hardness. Then, if the surface to be coated has irregularities or a foreign matter, delamination or cracking develops easily due to a mechanical or physical stress. If the carbon protective layer is formed after the surface of the underlying protective layer to be coated is smoothed by lapping treatment, the surface properties and the adhesion of the carbon protective layer are improved, so that image deterioration, cracking and delamination due to the irregularities on the surface can be effectively prevented (Unexamined Published Japanese Patent Application (KOKAI) No. 11-5323).
An object of the present invention is to provide a thermal head lapping apparatus that is capable of advantageously performing lapping treatment with a good efficiency on surfaces to be coated with protective layers or the formed protective layers in a process of fabricating a thermal head, thereby improving the production efficiency of the thermal head and fabricating with a good productivity the suitably lapped thermal head of high quality that ensures high quality image recording.
In order to achieve the above object, the invention provides a thermal head lapping apparatus comprising:
a pallet for holding at least one thermal head;
a transport device for transporting the thermal head held on the pallet successively to a specified processing position; and
a lapping device for forcing a lapping material being moved onto the thermal head that has been transported to said processing position.
In a preferred embodiment, said transport device moves the pallet in a direction in which heating elements of the thermal head are arranged while said lapping device forces the lapping material being moved onto the thermal head, so that the thermal head is lapped.
In another preferred embodiment, said pallet holds a plurality of thermal heads arranged in a direction perpendicular to a direction in which heating elements of each of the thermal heads are arranged; said lapping device uses the lapping material that has a width covering a whole area of the heating elements of each of the thermal heads; and said transport device transports the pallet discontinuously in the direction in which the thermal heads are arranged so that the thermal heads held on the pallet are successively transported to said processing position.